1. Field of the Invention
This invention relates in general to semiconductor dice and, in particular, to devices and methods for heating adhesives and other attachment materials to package or rework semiconductor dice.
2. State of the Art
Semiconductor dice are small, generally rectangular integrated circuit (IC) devices cut from a semiconductor wafer, such as a silicon wafer, on which multiple ICs have been fabricated. Bare dice are typically packaged to protect them from corrosion and physical damage by attaching them to a base, such as a lead frame or a printed circuit board, with a die-attach material, such as an epoxy or polyamide resin, cured in an oven, and then encapsulated in thermosetting plastic. In some instances, bare dice are attached to a printed circuit board and enclosed by a cover that is attached to the printed circuit board with an attachment material, such as a thermoset material, that requires additional curing in an oven.
This use of ovens for curing die-attach materials and attachment materials can be problematic for a number of reasons. Ovens are expensive to operate and take up precious room on the floor of a semiconductor manufacturing facility. Also, in addition to curing die-attach materials and attachment materials, ovens undesirably heat everything else on a printed circuit board or package as well, including solder joints, other adhesive joints, and other electronic devices. As a result, ovens can be destructive when sufficient care is not taken in their use. Further, because ovens cannot direct heat at individual dice or packages, they cannot be used to detach an individual die for reworking, or to detach a die cover from a package for reworking the die inside the package, without also detaching or destroying electronic devices that share a printed circuit board with the die.
In an attempt to eliminate the problems associated with heating semiconductor dice in an oven, in some instances, heaters have been embedded in printed circuit boards for use in the soldering of a semiconductor device to the printed circuit board and in attachment/disassembly operations. Such arrangements are shown in U.S. Pat. Nos. 5,010,233 and 5,175,409.
However, such prior art arrangements use heaters to heat large areas or the entirety of printed circuit boards or substrates, not specific localized areas of a predetermined configuration.
Therefore, there is a need in the art for a device that can direct heat at a specific area of an individual die or package to cure a die-attach material or attachment material associated therewith, or to loosen a previously cured die-attach material or attachment material associated therewith for detaching and reworking the die.
A system for attaching or removing for repair a bare die to a base, such as a lead frame, includes a heat-activated die-attach material, such as a suitable adhesive, interposed between a localized die-attach region on the base and the back surface of the die. A heating circuit, such as a thin-film resistor, integral with the base in substantial registry with the localized die-attach region generates heat in response to being electrically energized in order to activate the die-attach material. As a result, the system avoids the cumbersome use of ovens to heat the die-attach material. Instead, the system advantageously directs heat at the individual die to attach the die to the base by curing the die-attach material, or to detach the die from the base for rework by loosening the die-attach material.
In another embodiment of the present invention, a system for sealing a bare die in an enclosure, such as a Chip-Scale-Package, includes a heat-activated attachment material, such as a thermoset or thermoplastic material, interposed between the enclosure""s die cover and base at the interface therebetween. A heating circuit integral with either the base or the die cover in substantial registry with the interface therebetween generates heat in response to being electrically energized in order to activate the attachment material. As a result, the system advantageously directs heat at the interface between the enclosure""s die cover and base to attach the die cover to the base by curing the attachment material, or to detach the die cover from the base by loosening the attachment material for repair purposes.
In an additional embodiment, the previously summarized system for sealing a bare die in an enclosure includes a heat-activated, electrically resistive attachment material, such as a conductive epoxy adhesive, interposed between the die cover and the base in place of the heating circuit. In this embodiment, the attachment material itself generates heat in response to being electrically energized in order to attach or detach the die cover.